bug#78245: rm -d fails to remove non-empty directory

On 04/05/2025 11:35, Yannick Le Pennec wrote:
> Dear Maintainer,
> 
> On CephFS, creating a snapshot is done suchly:
>    $ mkdir .snap/snapshot-name
> 
> This creates a directory which contains a view of the current directory
> at the time the snapshot was created, and is therefore non-empty if the
> current directory was non-empty at that time. Its contents are immutable.
> 
> Removing a snapshot is done suchly:
>    $ rmdir .snap/snapshot-name
> 
> This works fine even if .snap/snapshot-name is non-empty, as rmdir calls
> rmdir(2) directly without trying to be smart, and the Ceph filesystem
> understands what rmdir on a snapshot directory means: remove the snapshot.
> 
> One would naturally expect rm -d to behave *exactly the same* as rmdir,
> but this isn't the case, because rm -d first does a getdents on the
> directory, observes it is non-empty, and refuses to perform the removal.
> 
>  From what I understand, this is non-compliant behavior per XCU rm 2.a. and 4.
> and XSH remove():
> 
> https://pubs.opengroup.org/onlinepubs/9799919799/utilities/rm.html
> 
>> 2. If file is of type directory, the following steps shall be taken:
>>    a. If neither the -R option nor the -r option is specified, but -d
>>    is specified, rm shall proceed with step 3 for the current file.
> 
>> 4. rm shall perform actions equivalent to the remove() function defined
>>    in the System Interfaces volume of POSIX.1-2024 called with a
>>    pathname of the current file used as the path argument.
> 
> https://pubs.opengroup.org/onlinepubs/9799919799/functions/remove.html
> 
>>    If path names a directory, remove(path) shall be equivalent to rmdir(path)
> 
> In short:
>     rm -d .snap/snapshot-name
> shall be equivalent to:
>     remove(".snap/snapshot-name")
> which in turn shall be equivalent to:
>     rmdir(".snap/snapshot-name")
> 
> Moreover other coreutils rm implementations (such as uutils or voreutils)
> do not exhibit this bug and correctly remove non-empty directories.
> 
> Regards,
> 
> Yannick Le Pennec

For reference this was also reported at:
https://bugs.debian.org/1104300